U.S. patent application number 11/962040 was filed with the patent office on 2009-06-25 for receiver adjustment between pilot bursts.
This patent application is currently assigned to QUALCOMM INCORPORATED. Invention is credited to Mingxi Fan, Jun Ma, Arash Mirbagheri.
Application Number | 20090161746 11/962040 |
Document ID | / |
Family ID | 40548798 |
Filed Date | 2009-06-25 |
United States Patent
Application |
20090161746 |
Kind Code |
A1 |
Mirbagheri; Arash ; et
al. |
June 25, 2009 |
RECEIVER ADJUSTMENT BETWEEN PILOT BURSTS
Abstract
A receiver may train its equalizer using consecutive pilot
bursts, divide the traffic between the consecutive pilot bursts
into multiple sub-segments, and interpolate the trained equalizer
coefficients to obtain the coefficients for equalizing one or more
of the sub-segments. The receiver may also determine signal to
interference and noise ratio (SINR) values based on each of the
consecutive pilot bursts, and interpolate the SINR for decoding one
or more of the sub-segments. The receiver may be an access terminal
receiver operating in a code division multiple access (CDMA)
cellular system.
Inventors: |
Mirbagheri; Arash; (San
Diego, CA) ; Ma; Jun; (San Diego, CA) ; Fan;
Mingxi; (San Diego, CA) |
Correspondence
Address: |
QUALCOMM INCORPORATED
5775 MOREHOUSE DR.
SAN DIEGO
CA
92121
US
|
Assignee: |
QUALCOMM INCORPORATED
San Diego
CA
|
Family ID: |
40548798 |
Appl. No.: |
11/962040 |
Filed: |
December 20, 2007 |
Current U.S.
Class: |
375/231 ;
375/346 |
Current CPC
Class: |
H04L 2025/03796
20130101; H04L 1/20 20130101; H04L 25/03019 20130101; H04L 25/03114
20130101; H04L 25/0232 20130101 |
Class at
Publication: |
375/231 ;
375/346 |
International
Class: |
H04L 27/01 20060101
H04L027/01; H04B 1/10 20060101 H04B001/10 |
Claims
1. A method for operating a receiver in a wireless communication
system, the method comprising steps of: receiving a frame including
a plurality of time slots, each time slot of the plurality of time
slots comprising two half-slots, each half-slot comprising two
traffic segments and a pilot burst between the two traffic
segments, wherein the plurality of time slots comprises a first
half-slot and a second half-slot following the first half-slot, the
first half-slot comprising a first pilot burst and a first traffic
segment following the first pilot burst, the second half-slot
comprising a second traffic segment and a second pilot burst
following the second traffic segment; dividing the first and second
traffic segments into a plurality of sub-segments, the plurality of
sub-segments comprising a first sub-segment and a second
sub-segment following the first sub-segment; training an equalizer
of the receiver on the first pilot burst to obtain a first
plurality of trained tap coefficients; training the equalizer of
the receiver on the second pilot burst to obtain a second plurality
of trained tap coefficients; interpolating between the first and
the second pluralities of trained tap coefficients to obtain a
first set of interpolated tap coefficients for the first
sub-segment; and equalizing the first sub-segment by using the
first set of interpolated tap coefficients.
2. The method of claim 1, wherein the first half-slot and the
second half-slot are not separated by any other half-slot, the
method further comprising providing at least some data in the
plurality of sub-segments to a user.
3. The method of claim 2, wherein the step of interpolating
comprises using linear interpolation.
4. The method of claim 2, wherein the step of interpolating
comprises using cubic interpolation.
5. The method of claim 2, wherein the step of interpolating
comprises combining linear interpolation with averaging.
6. The method of claim 2, wherein the step of dividing is performed
so that the second sub-segment comprises a first portion from the
first half-slot and a second portion from the second half-slot.
7. The method of claim 2, wherein: the first half-slot belongs to a
first time slot; the second half-slot belongs to a second time slot
following the first time slot; and the step of dividing is
performed so that the second sub-segment comprises a first portion
from the first half-slot and a second portion from the second
half-slot.
8. The method of claim 2, wherein the step of dividing is performed
so that the plurality of sub-segments further comprises a third
sub-segment preceding the first sub-segment, the method further
comprising steps of: interpolating between the first and the second
pluralities of trained tap coefficients to obtain a second set of
interpolated tap coefficients for the second sub-segment;
equalizing the second sub-segment by using the second set of
interpolated tap coefficients; interpolating between the first and
the second pluralities of trained tap coefficients to obtain a
third set of interpolated tap coefficients for the third
sub-segment; and equalizing the third sub-segment by using the
third set of interpolated tap coefficients.
9. The method of claim 2, wherein the step of dividing is performed
so that the plurality of sub-segments further comprises a third
sub-segment preceding the first sub-segment, the method further
comprising steps of: equalizing the second sub-segment by using the
second plurality of trained tap coefficients; and equalizing the
third sub-segment by using the first plurality of trained tap
coefficients.
10. The method of claim 2, further comprising steps of: determining
when a tap shift occurs in the equalizer between the first and the
second pilot burst; shifting equalizer coefficients in a direction
indicated by the tap shift prior to the step of training the
equalizer on the second pilot burst; and shifting equalizer history
in the direction indicated by the tap shift.
11. The method of claim 2, further comprising steps of: measuring
signal to interference and noise ratio of the first pilot burst to
obtain a first measured SINR; measuring signal to interference and
noise ratio of the second pilot burst to obtain a second measured
SINR; and interpolating between the first measured SINR and the
second measured SINR to obtain a first interpolated SINR for the
first sub-segment.
12. The method of claim 11, further comprising steps of: scaling
output of the equalizer corresponding to the first sub-segment by
the first interpolated SINR to obtain a first set of scaled data;
calculating a first log likelihood ratio of the first set of scaled
data; and decoding the first sub-segment using the first log
likelihood ratio.
13. The method of claim 12, wherein the step of interpolating
between the first measured SINR and the second measured SINR
comprises interpolating in linear domain.
14. The method of claim 12, wherein the step of dividing is
performed so that the plurality of sub-segments further comprises a
third sub-segment preceding the first sub-segment, the method
further comprising steps of: interpolating between the first
measured SINR and the second measured SINR to obtain a second
interpolated SINR for the second sub-segment; interpolating between
the first measured SINR and the second measured SINR to obtain a
third interpolated SINR for the third sub-segment; scaling output
of the equalizer corresponding to the second sub-segment by the
second interpolated SINR to obtain a second set of scaled data;
scaling output of the equalizer corresponding to the third
sub-segment by the third interpolated SINR to obtain a third set of
scaled data; calculating a log likelihood ratio of the second set
of scaled data; and calculating a log likelihood ratio of the third
set of scaled data.
15. The method of claim 12, wherein the step of dividing is
performed so that the plurality of sub-segments further comprises a
third sub-segment preceding the first sub-segment, the method
further comprising steps of: scaling output of the equalizer
corresponding to the second sub-segment by the second measured SINR
to obtain a second set of scaled data; scaling output of the
equalizer corresponding to the third sub-segment by the first
measured SINR to obtain a third set of scaled data; calculating a
log likelihood ratio of the second set of scaled data; and
calculating a log likelihood ratio of the third set of scaled
data.
16. A method for operating a receiver in a wireless communication
system, the method comprising steps of: receiving a frame including
a plurality of time slots, each time slot of the plurality of time
slots comprising two half-slots, each half-slot comprising two
traffic segments and a pilot burst between the two traffic
segments, wherein the plurality of time slots comprises a first
half-slot and a second half-slot following the first half-slot, the
first half-slot comprising a first pilot burst and a first traffic
segment following the first pilot burst, the second half-slot
comprising a second traffic segment and a second pilot burst
following the second traffic segment; dividing the first and second
traffic segments into a plurality of sub-segments, the plurality of
sub-segments comprising a first sub-segment and a second
sub-segment following the first sub-segment; measuring signal to
interference and noise ratio of the first pilot burst to obtain a
first measured SINR; measuring signal to interference and noise
ratio of the second pilot burst to obtain a second measured SINR;
interpolating between the first measured SINR and the second
measured SINR to obtain a first interpolated SINR for the first
sub-segment; and providing at least some data in the plurality of
sub-segments to a user.
17. The method of claim 16, wherein the receiver comprises an
equalizer, the method further comprising steps of: scaling output
of the equalizer corresponding to the first sub-segment by the
first interpolated SINR to obtain a first set of scaled data;
calculating a first log likelihood ratio of the first set of scaled
data; and decoding the first sub-segment using the first log
likelihood ratio.
18. The method of claim 17, wherein the step of interpolating
between the first measured SINR and the second measured SINR
comprises interpolating in linear domain.
19. The method of claim 17, wherein the plurality of sub-segments
further comprises a third sub-segment preceding the first
sub-segment, the method further comprising steps of: interpolating
between the first measured SINR and the second measured SINR to
obtain a second interpolated SINR for the second sub-segment;
interpolating between the first measured SINR and the second
measured SINR to obtain a third interpolated SINR for the third
sub-segment; scaling output of the equalizer corresponding to the
second sub-segment by the second interpolated SINR to obtain a
second set of scaled data; scaling output of the equalizer
corresponding to the third sub-segment by the third interpolated
SINR to obtain a third set of scaled data; calculating a log
likelihood ratio of the second set of scaled data; and calculating
a log likelihood ratio of the third set of scaled data.
20. The method of claim 17, wherein the plurality of sub-segments
further comprises a third sub-segment preceding the first
sub-segment, the method further comprising steps of: scaling output
of the equalizer corresponding to the second sub-segment by the
second measured SINR to obtain a second set of scaled data; scaling
output of the equalizer corresponding to the third sub-segment by
the first measured SINR to obtain a third set of scaled data;
calculating a log likelihood ratio of the second set of scaled
data; and calculating a log likelihood ratio of the third set of
scaled data.
21. A wireless terminal comprising: a receiver; a memory; and a
controller coupled to the receiver and the memory, the controller
is configured to: receive a plurality of time slots, each time slot
of the plurality of time-slots comprising two half-slots, each
half-slot comprising two traffic segments and a pilot burst between
the two traffic segments, wherein the plurality of time slots
comprises a first half-slot and a second half-slot following the
first half-slot, the first half-slot comprising a first pilot burst
and a first traffic segment following the first pilot burst, the
second half-slot comprising a second traffic segment and a second
pilot burst following the second traffic segment; divide the first
and the second traffic segments into a plurality of sub-segments,
the plurality of sub-segments comprising a first sub-segment and a
second sub-segment following the first sub-segment; train an
equalizer on the first pilot burst to obtain a first plurality of
trained tap coefficients; train the equalizer on the second pilot
burst to obtain a second plurality of trained tap coefficients;
interpolate between the first and the second pluralities of trained
tap coefficients to obtain a first set of interpolated tap
coefficients for the first sub-segment; and equalize the first
sub-segment by using the equalizer with the first set of
interpolated tap coefficients.
22. The wireless terminal of claim 21, wherein the first half-slot
and the second half-slot are not separated by any other half-slot,
and the controller is further configured to provide at least some
data in the three or more sub-segments to a user.
23. The wireless terminal of claim 22, wherein the controller is
configured to interpolate by using linear interpolation.
24. The wireless terminal of claim 22, wherein the controller is
configured to interpolate by using cubic interpolation.
25. The wireless terminal of claim 22, wherein the controller is
configured to interpolate by combining linear interpolation with
averaging.
26. The wireless terminal of claim 22, wherein the controller is
configured to divide so that the second sub-segment comprises a
first portion from the first half-slot and a second portion from
the second half-slot.
27. The wireless terminal of claim 22, wherein: the first half-slot
belongs to a first time slot; the second half-slot belongs to a
second time slot following the first time slot; and the controller
is configured to divide so that the second sub-segment comprises a
first portion from the first half-slot and a second portion from
the second half-slot.
28. The wireless terminal of claim 22, wherein the plurality of
sub-segments further comprises a third sub-segment preceding the
first sub-segment, and the controller is further configured to:
interpolate between the first and the second pluralities of trained
tap coefficients to obtain a second set of interpolated tap
coefficients for the second sub-segment; equalize the second
sub-segment by using the second set of interpolated tap
coefficients; interpolate between the first and the second
pluralities of trained tap coefficients to obtain a third set of
interpolated tap coefficients for the third sub-segment; and
equalize the third sub-segment by using the third set of
interpolated tap coefficients.
29. The wireless terminal of claim 22, wherein the plurality of
sub-segments further comprises a third sub-segment preceding the
first sub-segment, and the controller is further configured to:
equalize the second sub-segment by using the second plurality of
trained tap coefficients; and equalize the third sub-segment by
using the first plurality of trained tap coefficients.
30. The wireless terminal of claim 22, wherein the controller is
further configured to: determine when a tap shift occurs in the
equalizer between the first and the second pilot bursts; shift
equalizer coefficients in a direction indicated by the tap shift
prior to training the equalizer on the second pilot burst; and
shift equalizer history in the direction indicated by the tap
shift.
31. The wireless terminal of claim 22, wherein the controller is
further configured to: measure signal to interference and noise
ratio of the first pilot burst to obtain a first measured SINR;
measure signal to interference and noise ratio of the second pilot
burst to obtain a second measured SINR; and interpolate between the
first measured SINR and the second measured SINR to obtain a first
interpolated SINR for the first sub-segment.
32. The wireless terminal of claim 31, wherein the controller is
further configured to: scale output of the equalizer corresponding
to the first sub-segment by the first interpolated SINR to obtain a
first set of scaled data; calculate a first log likelihood ratio of
the first set of scaled data; and decode the first sub-segment
using the first log likelihood ratio.
33. The wireless terminal of claim 32, wherein interpolating
between the first measured SINR and the second measured SINR
comprises interpolating in linear domain.
34. The wireless terminal of claim 32, wherein the plurality of
sub-segments further comprises a third sub-segment preceding the
first sub-segment, and the controller is further configured to:
interpolate between the first measured SINR and the second measured
SINR to obtain a second interpolated SINR for the second
sub-segment; interpolate between the first measured SINR and the
second measured SINR to obtain a third interpolated SINR for the
third sub-segment; scale output of the equalizer corresponding to
the second sub-segment by the second interpolated SINR to obtain a
second set of scaled data; scale output of the equalizer
corresponding to the third sub-segment by the third interpolated
SINR to obtain a third set of scaled data; calculate a log
likelihood ratio of the second set of scaled data; and calculate a
log likelihood ratio of the third set of scaled data.
35. The wireless terminal of claim 32, wherein the plurality of
sub-segments further comprises a third sub-segment preceding the
first sub-segment, and the controller is further configured to:
scale output of the equalizer corresponding to the second
sub-segment by the second measured SINR to obtain a second set of
scaled data; scale output of the equalizer corresponding to the
third sub-segment by the first measured SINR to obtain a third set
of scaled data; calculate a log likelihood ratio of the second set
of scaled data; and calculate a log likelihood ratio of the third
set of scaled data.
36. A wireless terminal comprising: a receiver; a memory; and a
controller coupled to the receiver and the memory, the controller
is configured to: receive a plurality of time slots, each time slot
of the plurality of time-slots comprising two half-slots, each
half-slot comprising two traffic segments and a pilot burst between
the two traffic segments, wherein the plurality of time slots
comprises a first half-slot and a second half-slot following the
first half-slot, no half-slot separating the first half-slot and
the second half-slot, the first half-slot comprising a first pilot
burst and a first traffic segment following the first pilot burst,
the second half-slot comprising a second traffic segment and a
second pilot burst following the second traffic segment; divide the
first and the second traffic segments into a plurality of
sub-segments, the plurality of sub-segments comprising a first
sub-segment and a second sub-segment following the first
sub-segment; measure signal to interference and noise ratio of the
first pilot burst to obtain a first measured SINR; measure signal
to interference and noise ratio of the second pilot burst to obtain
a second measured SINR; interpolate between the first measured SINR
and the second measured SINR to obtain a first interpolated SINR
for the first sub-segment; and provide at least some data in the
plurality of sub-segments to a user.
37. The wireless terminal of claim 36, wherein the controller is
further configured to: scale equalizer output corresponding to the
first sub-segment by the first interpolated SINR to obtain a first
set of scaled data; calculate a first log likelihood ratio of the
first set of scaled data; and decode the first sub-segment using
the first log likelihood ratio.
38. The wireless terminal of claim 37, wherein the controller is
configured to interpolate between the first measured SINR and the
second measured SINR by interpolating in linear domain.
39. The wireless terminal of claim 37, wherein the plurality of
sub-segments further comprises a third sub-segment preceding the
first sub-segment, and the controller is further configured to:
interpolate between the first measured SINR and the second measured
SINR to obtain a second interpolated SINR for the second
sub-segment; interpolate between the first measured SINR and the
second measured SINR to obtain a third interpolated SINR for the
third sub-segment; scale equalizer output corresponding to the
second sub-segment by the second interpolated SINR to obtain a
second set of scaled data; scale equalizer output corresponding to
the third sub-segment by the third interpolated SINR to obtain a
third set of scaled data; calculate a log likelihood ratio of the
second set of scaled data; and calculate a log likelihood ratio of
the third set of scaled data.
40. The wireless terminal of claim 37, wherein the plurality of
sub-segments further comprises a third sub-segment preceding the
first sub-segment, and the controller is further configured to:
scale equalizer output corresponding to the second sub-segment by
the second measured SINR to obtain a second set of scaled data;
scale equalizer output corresponding to the third sub-segment by
the first measured SINR to obtain a third set of scaled data;
calculate a log likelihood ratio of the second set of scaled data;
and calculate a log likelihood ratio of the third set of scaled
data.
41. A wireless terminal comprising: a means for receiving a
wireless signal; a means for equalizing; a means for storing data;
and a means for processing, the means for processing being coupled
to the means for receiving, the means for equalizing, and the means
for storing, wherein the means for processing is configured to:
receive a plurality of time slots, each time slot of the plurality
of time-slots comprising two half-slots, each half-slot comprising
two traffic segments and a pilot burst between the two traffic
segments, wherein the plurality of time slots comprises a first
half-slot and a second half-slot following the first half-slot, no
half-slot separating the first half-slot and the second half-slot,
the first half-slot comprising a first pilot burst and a first
traffic segment following the first pilot burst, the second
half-slot comprising a second traffic segment and a second pilot
burst following the second traffic segment; divide the first and
the second traffic segments into a plurality of sub-segments, the
plurality of sub-segments comprising a first sub-segment and a
second sub-segment following the first sub-segment; train the means
for equalizing on the first pilot burst to obtain a first plurality
of trained tap coefficients; train the means for equalizing on the
second pilot burst to obtain a second plurality of trained tap
coefficients; interpolate between the first and the second
pluralities of trained tap coefficients to obtain a first set of
interpolated tap coefficients for the first sub-segment; equalize
the first sub-segment by using the first set of interpolated tap
coefficients; and provide at least some data in the plurality of
sub-segments to a user.
42. A wireless terminal comprising: a means for receiving a
wireless signal; a means for equalizing; a means for storing data;
and a means for processing, the means for processing being coupled
to the means for receiving, the means for equalizing, and the means
for storing, wherein the means for processing is configured to:
receive a plurality of time slots, each time slot of the plurality
of time-slots comprising two half-slots, each half-slot comprising
two traffic segments and a pilot burst between the two traffic
segments, wherein the plurality of time slots comprises a first
half-slot and a second half-slot following the first half-slot, no
half-slot separating the first half-slot and the second half-slot,
the first half-slot comprising a first pilot burst and a first
traffic segment following the first pilot burst, the second
half-slot comprising a second traffic segment and a second pilot
burst following the second traffic segment; divide the first and
the second traffic segments into a plurality of sub-segments, the
plurality of sub-segments comprising a first sub-segment and a
second sub-segment following the first sub-segment; measure signal
to interference and noise ratio of the first pilot burst to obtain
a first measured SINR; measure signal to interference and noise
ratio of the second pilot burst to obtain a second measured SINR;
interpolate between the first measured SINR and the second measured
SINR to obtain a first interpolated SINR for the first sub-segment;
and provide at least some data in the plurality of sub-segments to
a user.
43. A machine-readable medium comprising instructions, the
instructions, when executed by at least one processor of a wireless
access terminal, cause the access terminal to perform steps
comprising: receiving a plurality of time slots, each time slot of
the plurality of time-slots comprising two half-slots, each
half-slot comprising two traffic segments and a pilot burst between
the two traffic segments, wherein the plurality of time slots
comprises a first half-slot and a second half-slot following the
first half-slot, the first half-slot comprising a first pilot burst
and a first traffic segment following the first pilot burst, the
second half-slot comprising a second traffic segment and a second
pilot burst following the second traffic segment; dividing the
first and the second traffic segments into a plurality of
sub-segments, the plurality of sub-segments comprising a first
sub-segment and a second sub-segment following the first
sub-segment; training an equalizer on the first pilot burst to
obtain a first plurality of trained tap coefficients; training the
equalizer on the second pilot burst to obtain a second plurality of
trained tap coefficients; interpolating between the first and the
second pluralities of trained tap coefficients to obtain a first
set of interpolated tap coefficients for the first sub-segment; and
equalizing the first sub-segment by using the first set of
interpolated tap coefficients.
44. The machine-readable medium of claim 43, wherein: the first
half-slot and the second half-slot are not separated by any other
half-slot; and the steps further comprise providing at least some
data in the plurality of sub-segments to a user.
45. The machine-readable medium of claim 44, wherein the step of
interpolating comprises using linear interpolation.
46. The machine-readable medium of claim 44, wherein the step of
interpolating comprises using cubic interpolation.
47. The machine-readable medium of claim 44, wherein the step of
interpolating comprises combining interpolation with averaging.
48. The machine-readable medium of claim 44, wherein the step of
dividing is performed so that the second sub-segment comprises a
first portion from the first half-slot and a second portion from
the second half-slot.
49. The machine-readable medium of claim 44, wherein: the first
half-slot belongs to a first time slot; the second half-slot
belongs to a second time slot following the first time slot; and
the step of dividing is performed so that the second sub-segment
comprises a first portion from the first half-slot and a second
portion from the second half-slot.
50. The machine-readable medium of claim 44, wherein the plurality
of sub-segments further comprises a third sub-segment preceding the
first sub-segment, and the steps further comprise: interpolating
between the first and the second pluralities of trained tap
coefficients to obtain a second set of interpolated tap
coefficients for the second sub-segment; equalizing the second
sub-segment by using the second set of interpolated tap
coefficients; interpolating between the first and the second
pluralities of trained tap coefficients to obtain a third set of
interpolated tap coefficients for the third sub-segment; and
equalizing the third sub-segment by using the third set of
interpolated tap coefficients.
51. The machine-readable medium of claim 44, wherein the plurality
of sub-segments further comprises a third sub-segment preceding the
first sub-segment, and the steps further comprise: equalizing the
second sub-segment by using the second plurality of trained tap
coefficients; and equalizing the third sub-segment by using the
first plurality of trained tap coefficients.
52. The machine-readable medium of claim 44, wherein the steps
further comprise: determining when a tap shift occurs in the
equalizer between the first and the second pilot bursts; shifting
equalizer coefficients in a direction indicated by the tap shift
prior to the step of training the equalizer of the receiver on the
second pilot burst; and shifting equalizer history in the direction
indicated by the tap shift.
53. The machine-readable medium of claim 44, wherein the steps
further comprise: measuring signal to interference and noise ratio
of the first pilot burst to obtain a first measured SINR; measuring
signal to interference and noise ratio of the second pilot burst to
obtain a second measured SINR; and interpolating between the first
measured SINR and the second measured SINR to obtain a first
interpolated SINR for the first sub-segment.
54. The machine-readable medium of claim 53, wherein the steps
further comprise: scaling output of the equalizer corresponding to
the first sub-segment by the first interpolated SINR to obtain a
first set of scaled data; calculating a first log likelihood ratio
of the first set of scaled data; and decoding the first sub-segment
using the first log likelihood ratio.
55. The machine-readable medium of claim 54, wherein the step of
interpolating between the first measured SINR and the second
measured SINR comprises interpolating in linear domain.
56. The machine-readable medium of claim 54, wherein the plurality
of sub-segments further comprises a third sub-segment preceding the
first sub-segment, and the steps further comprise: interpolating
between the first measured SINR and the second measured SINR to
obtain a second interpolated SINR for the second sub-segment;
interpolating between the first measured SINR and the second
measured SINR to obtain a third interpolated SINR for the third
sub-segment; scaling output of the equalizer corresponding to the
second sub-segment by the second interpolated SINR to obtain a
second set of scaled data; scaling output of the equalizer
corresponding to the third sub-segment by the third interpolated
SINR to obtain a third set of scaled data; calculating a log
likelihood ratio of the second set of scaled data; and calculating
a log likelihood ratio of the third set of scaled data.
57. The machine-readable medium of claim 54, wherein the plurality
of sub-segments further comprises a third sub-segment preceding the
first sub-segment, and the steps further comprise: scaling output
of the equalizer corresponding to the second sub-segment by the
second measured SINR to obtain a second set of scaled data; scaling
output of the equalizer corresponding to the third sub-segment by
the first measured SINR to obtain a third set of scaled data;
calculating a log likelihood ratio of the second set of scaled
data; and calculating a log likelihood ratio of the third set of
scaled data.
58. A machine-readable medium comprising instructions, the
instructions, when executed by at least one processor of a wireless
access terminal, cause the wireless access terminal to perform
steps comprising: receiving a plurality of time slots, each time
slot of the plurality of time-slots comprising two half-slots, each
half-slot comprising two traffic segments and a pilot burst between
the two traffic segments, wherein the plurality of time slots
comprises a first half-slot and a second half-slot following the
first half-slot, no half-slot separating the first half-slot and
the second half-slot, the first half-slot comprising a first pilot
burst and a first traffic segment following the first pilot burst,
the second half-slot comprising a second traffic segment and a
second pilot burst following the second traffic segment; dividing
the first and the second traffic segments into a plurality of
sub-segments, the plurality of sub-segments comprising a first
sub-segment and a second sub-segment following the first
sub-segment; measuring signal to interference and noise ratio of
the first pilot burst to obtain a first measured SINR; measuring
signal to interference and noise ratio of the second pilot burst to
obtain a second measured SINR; interpolating between the first
measured SINR and the second measured SINR to obtain a first
interpolated SINR for the first sub-segment; and providing at least
some data in the plurality of sub-segments to a user.
59. The machine-readable medium of claim 58, wherein the steps
further comprise: scaling output of the equalizer corresponding to
the first sub-segment by the first interpolated SINR to obtain a
first set of scaled data; calculating a first log likelihood ratio
of the first set of scaled data; and decoding the first sub-segment
using the second log likelihood ratio.
60. The machine-readable medium of claim 59, wherein the step of
interpolating between the first measured SINR and the second
measured SINR comprises interpolating in linear domain.
61. The machine-readable medium of claim 59, wherein the plurality
of sub-segments further comprises a third sub-segment preceding the
first sub-segment, and the steps further comprise: interpolating
between the first measured SINR and the second measured SINR to
obtain a second interpolated SINR for the second sub-segment;
interpolating between the first measured SINR and the second
measured SINR to obtain a third interpolated SINR for the third
sub-segment; scaling output of the equalizer corresponding to the
second sub-segment by the second interpolated SINR to obtain a
second set of scaled data; scaling output of the equalizer
corresponding to the third sub-segment by the third interpolated
SINR to obtain a third set of scaled data; calculating a log
likelihood ratio of the second set of scaled data; and calculating
a log likelihood ratio of the third set of scaled data.
62. The machine-readable medium of claim 59, wherein the plurality
of sub-segments further comprises a third sub-segment preceding the
first sub-segment, and the steps further comprise: scaling output
of the equalizer corresponding to the second sub-segment by the
second measured SINR to obtain a second set of scaled data; scaling
output of the equalizer corresponding to the third sub-segment by
the first measured SINR to obtain a third set of scaled data;
calculating a log likelihood ratio of the second set of scaled
data; and calculating a log likelihood ratio of the third set of
scaled data.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to wireless
communications. More particularly, the invention relates to
adjustment of equalizer tap coefficients and signal to interference
and noise ratio estimates in a receiver.
BACKGROUND
[0002] A modern communication system is expected to provide
reliable data transmission for a variety of applications, such as
voice and data applications. In a point-to-multipoint
communications context, known communication systems are based on
frequency division multiple access (FDMA), time division multiple
access (TDMA), code division multiple access (CDMA), and perhaps
other multiple access communication schemes.
[0003] A CDMA system may be designed to support one or more CDMA
standards, such as (1) the "TIA/EIA-95 Mobile Station-Base Station
Compatibility Standard for Dual-Mode Wideband Spread Spectrum
Cellular System" (this standard with its enhanced revisions A and B
may be referred to as the "IS-95 standard"), (2) the "TIA/EIA-98-C
Recommended Minimum Standard for Dual-Mode Wideband Spread Spectrum
Cellular Mobile Station" (the "IS-98 standard"), (3) the standard
sponsored by a consortium named "3rd Generation Partnership
Project" (3GPP) and embodied in a set of documents known as the
"W-CDMA standard," (4) the standard sponsored by a consortium named
"3rd Generation Partnership Project 2" (3GPP2) and embodied in a
set of documents including "TR-45.5 Physical Layer Standard for
cdma2000 Spread Spectrum Systems," the "C.S0005-A Upper Layer
(Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems,"
and the "TIA/EIA/IS-856 cdma2000 High Rate Packet Data Air
Interface Specification" (the "cdma2000 standard" collectively),
(5) the 1xEV-DO standard, and (6) certain other standards.
[0004] A wireless access terminal, for example, a terminal in a
wireless CDMA system, may receive data transmissions from one or
more base stations on forward link or links. The signal transmitted
by a particular base station may reach the terminal through
multiple propagation paths. The received signal at the terminal may
include one or more signal instances (also known as multipath
components) of the signal transmitted by the base station. The word
"multipath" refers to the existence of multiple propagation paths
along which a signal travels from a transmitter (e.g., a base
station) to a receiver (e.g., an access terminal). Each of the
multipath components is also subjected to the varying physical
channel response, noise, and interference. The terminal may employ
an equalizer to compensate for the channel response and the
multipath distortion. An equalizer may be an equalization filter
with a number of delay elements and multiplication coefficients at
taps corresponding to the delay elements. Some equalization
techniques and equalizers are described in a commonly-assigned U.S.
Pat. No. 7,301,990, entitled Equalization of Multiple Signals
Received for Soft Handoff in Wireless Communication Systems; and in
a commonly assigned U.S. Pat. No. 6,522,683, entitled Method and
Apparatus for Adaptive Linear Equalization for Walsh Covered
Modulation.
[0005] Pilot signals may be used for estimating the physical
channel between a transmitter and a receiver, for example, from the
base station to the access terminal in the CDMA system. A pilot
signal is a signal carrying a predefined data sequence, so that
distortion of the pilot can be attributed to the transmission
channel, and the transmission channel can thus be estimated from
the received pilot.
[0006] The pilot may be transmitted at well defined, periodic
intervals of the forward link. In some CDMA systems, for example, a
forward link is defined in terms of frames. A frame may include
sixteen time slots. Each time slot may be 2048 chips long,
corresponding to a 1.67 millisecond slot duration, and,
consequently, a frame with 26.67 millisecond duration. Each slot
may be divided into two half-slots, with a pilot burst of 96 chips
transmitted in the middle of each half-slot. The remainder of each
half-slot is occupied by two traffic carrying portions of about 400
chips each, and media access control (MAC) portions.
[0007] With each pilot burst, the equalizer is trained and its tap
coefficients are adapted based on the estimate obtained with the
pilot burst. The coefficients thus obtained are then used to
demodulate the traffic portions on each side of the pilot burst.
Because the coefficients obtained from training on a particular
pilot burst are used to demodulate traffic following the pilot
burst in time, the method is anti-causal.
[0008] In fast changing channel conditions, the channel may undergo
a substantial variation between the time of the pilot burst and the
actual transmission and receipt of data, particularly for the data
that is most distant in time from the pilot burst. Proper equalizer
training is important for equalizer performance and, consequently,
for receiver performance. Therefore, there is a need in the art for
apparatus, methods, and articles of manufacture that improve
matching of equalizer coefficients to the actual transmission
channel conditions at the time of the data transmission and
receipt. There is also a need in the art for receivers with such
improved equalizers. There is a further need in the art for
wireless communication systems that employ such receivers.
[0009] Signal to noise and interference ratio (SINR) for the signal
is measured during pilot bursts as well, and then used for scaling
equalizer output before feeding it to a block that calculates log
likelihood ratio, and/or for other processing of the transmitted
information. Consequently, obtaining good SINR estimates is also
important for receiver performance. Therefore, there is a need in
the art for apparatus, methods, and articles of manufacture that
improve SINR estimates of the actual transmission channel
conditions at the time of the data transmission and receipt. There
is also a need in the art for receivers that use such improved SINR
estimates. There is a further need in the art for wireless
communication systems that employ such receivers.
SUMMARY
[0010] Embodiments disclosed herein may address one or more of the
above stated needs by providing apparatus, methods, and articles of
manufacture for interpolating equalizer coefficients and/or SINR
estimates between pilot bursts. The systems, methods, and articles
of manufacture described below may be employed in
telecommunications, including uses in cellular access
terminals.
[0011] A method is described for operating a receiver in a wireless
communication system. The method includes receiving a frame
including a plurality of time slots. Each time slot of the
plurality of time slots has two half-slots, each half-slot
including two traffic segments and a pilot burst between the two
traffic segments. The plurality of time slots includes a first
half-slot and a second half-slot following the first half-slot. The
first half-slot has a first pilot burst and a first traffic segment
following the first pilot burst. The second half-slot has a second
traffic segment and a second pilot burst following the second
traffic segment. The method also includes dividing the first and
second traffic segments into a plurality of sub-segments. The
plurality of sub-segments includes a first sub-segment and a second
sub-segment following the first sub-segment. The method further
includes training an equalizer of the receiver on the first pilot
burst to obtain a first plurality of trained tap coefficients, and
training the equalizer of the receiver on the second pilot burst to
obtain a second plurality of trained tap coefficients. The method
further includes interpolating between the first and the second
pluralities of trained tap coefficients to obtain a first set of
interpolated tap coefficients for the first sub-segment, and
equalizing the first sub-segment by using the first set of
interpolated tap coefficients.
[0012] Another method for operating a receiver in a wireless
communication system includes receiving a frame with a plurality of
time slots, each time slot of the plurality of time slots having
two half-slots. Each of the half-slots has two traffic segments and
a pilot burst between the two traffic segments. The plurality of
time slots includes a first half-slot and a second half-slot
following the first half-slot. The first half-slot includes a first
pilot burst and a first traffic segment following the first pilot
burst, and the second half-slot includes a second traffic segment
and a second pilot burst following the second traffic segment. The
method also includes dividing the first and second traffic segments
into a plurality of sub-segments. The plurality of sub-segments has
a first sub-segment and a second sub-segment following the first
sub-segment. The method further includes measuring signal to
interference and noise ratio of the first pilot burst to obtain a
first measured SINR, and measuring signal to interference and noise
ratio of the second pilot burst to obtain a second measured SINR.
The method further includes interpolating between the first
measured SINR and the second measured SINR to obtain a first
interpolated SINR for the first sub-segment. The method further
includes providing at least some data in the plurality of
sub-segments to a user.
[0013] A wireless terminal is described. the wireless terminal
includes a receiver, a memory, and a controller coupled to the
receiver and the memory. The controller is configured to receive a
plurality of time slots, each time slot of the plurality of
time-slots including two half-slots. Each half-slot has two traffic
segments and a pilot burst between the two traffic segments. The
plurality of time slots includes a first half-slot and a second
half-slot following the first half-slot. The first half-slot has a
first pilot burst and a first traffic segment following the first
pilot burst. The second half-slot has a second traffic segment and
a second pilot burst following the second traffic segment. The
controller is also configured to divide the first and the second
traffic segments into a plurality of sub-segments. The plurality of
sub-segments includes a first sub-segment and a second sub-segment
following the first sub-segment. The controller is also configured
to train an equalizer on the first pilot burst to obtain a first
plurality of trained tap coefficients, and to train the equalizer
on the second pilot burst to obtain a second plurality of trained
tap coefficients. The controller is further configured to
interpolate between the first and the second pluralities of trained
tap coefficients to obtain a first set of interpolated tap
coefficients for the first sub-segment. The controller is further
configured to equalize the first sub-segment by using the equalizer
with the first set of interpolated tap coefficients.
[0014] A wireless terminal is described. The wireless terminal
includes a receiver, a memory, and a controller coupled to the
receiver and the memory. The controller is configured to receive a
plurality of time slots, each time slot of the plurality of
time-slots having two half-slots. Each half-slot includes two
traffic segments and a pilot burst between the two traffic
segments. The plurality of time slots includes a first half-slot
and a second half-slot following the first half-slot, with no
half-slot separating the first half-slot and the second half-slot.
The first half-slot includes a first pilot burst and a first
traffic segment following the first pilot burst, and the second
half-slot includes a second traffic segment and a second pilot
burst following the second traffic segment. The controller is also
configured to divide the first and the second traffic segments into
a plurality of sub-segments. The plurality of sub-segments includes
a first sub-segment and a second sub-segment following the first
sub-segment. The controller is further configured to measure signal
to interference and noise ratio of the first pilot burst to obtain
a first measured SINR, and to measure signal to interference and
noise ratio of the second pilot burst to obtain a second measured
SINR. The controller is further configured to interpolate between
the first measured SINR and the second measured SINR to obtain a
first interpolated SINR for the first sub-segment. The controller
is further configured to provide at least some data in the
plurality of sub-segments to a user.
[0015] A wireless terminal is described. The wireless terminal
includes a means for receiving a wireless signal, a means for
equalizing, a means for storing data, and a means for processing.
The means for processing is coupled to the means for receiving, the
means for equalizing, and the means for storing. The means for
processing is configured to receive a plurality of time slots, each
time slot of the plurality of time-slots having two half-slots.
Each of the half-slots has two traffic segments and a pilot burst
between the two traffic segments. The plurality of time slots
includes a first half-slot and a second half-slot following the
first half-slot, with no half-slot separating the first half-slot
and the second half-slot. The first half-slot includes a first
pilot burst and a first traffic segment following the first pilot
burst, and the second half-slot includes a second traffic segment
and a second pilot burst following the second traffic segment. The
controller is also configured to divide the first and the second
traffic segments into a plurality of sub-segments. The plurality of
sub-segments includes a first sub-segment and a second sub-segment
following the first sub-segment. The controller is further
configured to train the means for equalizing on the first pilot
burst to obtain a first plurality of trained tap coefficients, and
to train the means for equalizing on the second pilot burst to
obtain a second plurality of trained tap coefficients. The
controller is further configured to interpolate between the first
and the second pluralities of trained tap coefficients to obtain a
first set of interpolated tap coefficients for the first
sub-segment. The controller is further configured to equalize the
first sub-segment by using the first set of interpolated tap
coefficients. The controller is further configured to provide at
least some data in the plurality of sub-segments to a user.
[0016] A wireless terminal is described. The wireless terminal
includes a means for receiving a wireless signal, a means for
equalizing, a means for storing data, and a means for processing.
The means for processing is coupled to the means for receiving, the
means for equalizing, and the means for storing. The means for
processing is configured to receive a plurality of time slots, each
time slot of the plurality of time-slots having two half-slots.
Each of the half-slots has two traffic segments and a pilot burst
between the two traffic segments. The plurality of time slots
includes a first half-slot and a second half-slot following the
first half-slot, with no half-slots separating the first half-slot
and the second half-slot. The first half-slot includes a first
pilot burst and a first traffic segment following the first pilot
burst. The second half-slot includes a second traffic segment and a
second pilot burst following the second traffic segment. The
controller is also configured to divide the first and the second
traffic segments into a plurality of sub-segments. The plurality of
sub-segments includes a first sub-segment and a second sub-segment
following the first sub-segment. The controller is further
configured to measure signal to interference and noise ratio of the
first pilot burst to obtain a first measured SINR, and to measure
signal to interference and noise ratio of the second pilot burst to
obtain a second measured SINR. The controller is further configured
to interpolate between the first measured SINR and the second
measured SINR to obtain a first interpolated SINR for the first
sub-segment. The controller is further configured to provide at
least some data in the plurality of sub-segments to a user.
[0017] A machine-readable medium is described. The medium stores
instructions. When the instructions are executed by at least one
processor of a wireless access terminal, they cause the access
terminal to perform a number of steps. The steps include receiving
a plurality of time slots, each time slot of the plurality of
time-slots having two half-slots. Each of the half-slots includes
two traffic segments and a pilot burst between the two traffic
segments. The plurality of time slots includes a first half-slot
and a second half-slot following the first half-slot. The first
half-slot includes a first pilot burst and a first traffic segment
following the first pilot burst. The second half-slot includes a
second traffic segment and a second pilot burst following the
second traffic segment. The steps also include dividing the first
and the second traffic segments into a plurality of sub-segments.
The plurality of sub-segments has a first sub-segment and a second
sub-segment following the first sub-segment. The steps further
include training an equalizer on the first pilot burst to obtain a
first plurality of trained tap coefficients, and training the
equalizer on the second pilot burst to obtain a second plurality of
trained tap coefficients. The steps further include interpolating
between the first and the second pluralities of trained tap
coefficients to obtain a first set of interpolated tap coefficients
for the first sub-segment. The steps further include equalizing the
first sub-segment by using the first set of interpolated tap
coefficients.
[0018] A machine-readable medium is described. The medium stores
instructions. When the instructions are executed by at least one
processor of a wireless access terminal, the instructions cause the
wireless access terminal to perform a number of steps. The steps
include receiving a plurality of time slots, each time slot of the
plurality of time-slots having two half-slots. Each of the
half-slots includes two traffic segments and a pilot burst between
the two traffic segments. The plurality of time slots includes a
first half-slot and a second half-slot following the first
half-slot, with no half-slot separating the first half-slot and the
second half-slot. The first half-slot includes a first pilot burst
and a first traffic segment following the first pilot burst. The
second half-slot includes a second traffic segment and a second
pilot burst following the second traffic segment. The steps also
include dividing the first and the second traffic segments into a
plurality of sub-segments. The plurality of sub-segments includes a
first sub-segment and a second sub-segment following the first
sub-segment. The steps further include measuring signal to
interference and noise ratio of the first pilot burst to obtain a
first measured SINR, and measuring signal to interference and noise
ratio of the second pilot burst to obtain a second measured SINR.
The steps further include interpolating between the first measured
SINR and the second measured SINR to obtain a first interpolated
SINR for the first sub-segment. The steps further include providing
at least some data in the plurality of sub-segments to a user.
[0019] These and other aspects of the present invention will be
better understood with reference to the following description,
drawings, and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 illustrates selected components of a communication
network in which a receiver interpolates equalizer coefficients
and/or SINR values;
[0021] FIG. 2 illustrates selected elements of frames of a forward
link wherein traffic half-slots are sub-segmented for interpolation
of equalizer coefficients and/or SINR values;
[0022] FIG. 3 illustrates selected elements of frames of a forward
link wherein traffic half-slots are sub-segmented for interpolation
of equalizer coefficients and/or SINR values, and wherein a
sub-segment crosses a segment boundary, a half-slot boundary, and a
time-slot boundary; and
[0023] FIG. 4 illustrates selected steps of a process for operating
a receiver with tap coefficients and SINR interpolation.
DETAILED DESCRIPTION
[0024] In this document, the words "embodiment," "variant," and
similar expressions are used to refer to particular apparatus,
process, or article of manufacture, and not necessarily to the same
apparatus, process, or article of manufacture. Thus, "one
embodiment" (or a similar expression) used in one place or context
may refer to a particular apparatus, process, or article of
manufacture; the same or a similar expression in a different place
may refer to a different apparatus, process, or article of
manufacture. The expressions "alternative embodiment,"
"alternatively," and similar phrases may be used to indicate one of
a number of different possible embodiments. The number of possible
embodiments is not necessarily limited to two or any other
quantity.
[0025] The concept of "interpolation" signifies any process of
calculating (approximating or estimating) a new point between two
existing data points, based on the existing data points.
[0026] An access terminal, which also may be referred to as AT,
subscriber station, user equipment, UE, mobile terminal, MT, or
cellular communication device may be mobile or stationary, and may
communicate with one or more base transceiver stations. An access
terminal may be any of a number of types of devices, including but
not limited to personal computer (PC) card, external or internal
modem, wireless telephone, and personal digital assistant (PDA)
with wireless communication capability. An access terminal
transmits and receives data packets to or from a radio network
controller through one or more base transceiver stations.
[0027] Base transceiver stations and base station controllers are
parts of a network called radio network, RN, access network, or AN.
A radio network may be a UTRAN or UMTS Terrestrial Radio Access
Network. The radio network may transport data packets between
multiple access terminals. The radio network may be further
connected to additional networks outside the radio network, such as
a corporate intranet, the Internet, a public switched telephone
network (PSTN), or another radio network, and may transport data
and voice packets between each access terminal and such outside
networks. Depending on conventions and on the specific
implementations, a base transceiver station may be referred to by
other names, including Node-B, base station system (BSS), and
simply base station. Similarly, a base station controller may be
referred to by other names, including radio network controller,
RNC, controller, mobile switching center, or serving GPRS support
node.
[0028] The scope of the invention extends to these and similar
wireless communication system components, as well as to other
electronic equipment.
[0029] The word "exemplary" may be used herein to mean "serving as
an example, instance, or illustration." Any embodiment or variant
described herein as "exemplary" is not necessarily to be construed
as preferred or advantageous over other embodiments or variants.
All of the embodiments and variants described in this description
are exemplary embodiments and variants provided to enable persons
skilled in the art to make and use the invention, and not
necessarily to limit the scope of legal protection afforded the
invention.
[0030] FIG. 1 illustrates selected components of a communication
network 100, which includes a radio network controller 110 coupled
to wireless base transceiver stations 120A, 120B, and 120C. The
base transceiver stations 120 communicate with access terminals
130A, 130B, 130C, and 130D through wireless connections 140A
through 140E. The radio network controller 110 is coupled to a
public switched telephone network 150 through a telephone switch
160, and to a packet switched network 170 through a packet data
server node ("PDSN") 180. Data interchange between various network
elements, such as the radio network controller 110 and the packet
data server node 180, can be implemented using any number of
protocols, for example, the Internet Protocol ("IP"), an
asynchronous transfer mode ("ATM") protocol, T1, E1, frame relay,
and other protocols.
[0031] The communication network 100 may provide both data
communication services and cellular telephone services to the
access terminals 130. Alternatively, the communication network 100
may provide only data services or only telephone services.
[0032] Multiple or even all the access terminals 130 may be in the
same cell or site, or each access terminal 130 may be in a separate
cell or site.
[0033] A typical access terminal, for example, the access terminal
130A, includes receive circuitry 131, transmitter circuitry 132,
encoder 133, decoder 134, equalizer 135, processor 136, and memory
device 137. The access terminal may also include or be connected to
one or more user interface devices, such as a microphone, a
speaker, a display, or a key pad. The receiver, transmitter,
encoder, decoder, and equalizer are configured by the processor
executing code stored in the memory device. Each access terminal
130 is configured to communicate data using at least one
transmission protocol, such as the wireless packet transmission
protocols described above. The access terminals 130 communicate
with the base transceiver stations 120 via communication channels
140A through 140E, as shown in FIG. 1. Each communication channel
140 may include both a forward link and a reverse link to a
corresponding access terminal 130.
[0034] Each of the base transceiver stations 120 includes one or
more wireless receivers (e.g., the receiver 121 of the BTS 120A),
one or more wireless transmitters (e.g., the transmitter 122 of the
BTS 120A), radio network controller interface (e.g., the interface
123), a memory (e.g., the memory 124), a processor (e.g., the
processor 125), and encoder/decoder circuitry (e.g., the
encoder/decoder circuitry 126). A receiver/transmitter pair of each
base transceiver station is configured by the station's processor
operating under control of program code stored in the BTS's memory,
to establish forward and reverse links with the access terminals
130 in order to send data packets to and receive data packets from
the access terminals 130. In the case of data services, for
example, the base transceiver stations 120 receive forward link
data packets from the packet switched network 170 through the
packet data server node 180 and through the radio network
controller 110, and transmit these packets to the access terminals
130. The base transceiver stations 120 receive reverse link data
packets that originate at the access terminals 130, and forward
these packets to the packet switched network 170 through the radio
network controller 110 and the packet data server node 180. In the
case of telephone services, the base transceiver stations 120
receive forward link data packets from the telephone network 150
through the telephone switch 160 and through the radio network
controller 110, and transmit these packets to the access terminals
130. Voice carrying packets originating at the access terminals 130
are received at the base transceiver stations 120 and forwarded to
the telephone network 150 via the radio network controller 110 and
the telephone switch 160.
[0035] Alternatively, the transmitter and the receiver of the BTSs
may have one or more separate processors each.
[0036] The radio network controller 110 includes one or more
interfaces 111 to the base transceiver stations 120, an interface
112 to the packet data server node 180, and an interface 113 to the
telephone switch 160. The interfaces 111, 112, and 113 operate
under control of one or more processors 114 executing program code
stored in a memory device 115.
[0037] As illustrated in FIG. 1, the network 100 includes one
public switched telephone network, one packet switched network, one
base station controller, three base transceiver stations, and four
access terminals. A person skilled in the art would recognize,
after perusal of this document, that alternatively networks need
not be limited to any particular number of these components. For
example, a lesser or a greater number of base transceiver stations
and access terminals may be included. Furthermore, the
communication network 100 can connect the access terminals 130 to
one or more additional communication networks, for example, a
second wireless communication network having a number of wireless
access terminals.
[0038] FIG. 2 shows frames 210A, 210B, and 210C of a channel of a
forward link 200 between a selected BTS 120 and a selected access
terminals 130. The selected BTS may be the BTS 120A, and the
selected access terminal may be the access terminal 130A; for
simplicity, from now on we will refer to these network devices
simply as the BTS 120 and the access terminal 130, respectively.
Note that although only three frames are shown in FIG. 2, many
additional frames may be, and typically are, present. In an
exemplary system, each frame has sixteen time slots, each time slot
being 2048 chips long and corresponding to 1.67 millisecond slot
duration; each frame thus is 26.67 milliseconds in duration. The
time slots of the frame 210B include consecutive time slots 220 and
240, which are shown in additional detail. Note that other time
slots would appear the same or substantially the same at this level
of abstraction.
[0039] Each slot is divided into two half-slots, with a pilot
bursts transmitted in the middle of each half-slot. The time slot
220 thus has half-slots 220A and 220B, with a pilot burst 223 in
the middle of the half-slot 220A, and another pilot burst 227 in
the middle of the half-slot 220B; the time slot 240 similarly has
half-slots 240A and 240B, with pilot bursts 243 and 247,
respectively. Each pilot burst is surrounded by MAC portions 221.
Each combination of a pilot burst with its surrounding MAC portions
breaks the corresponding half-slot into two traffic carrying
segments. Here, "traffic" refers to data other than pilot bursts
and MAC portions; traffic typically includes payload data. As shown
in FIG. 2, the segments of the time slots 220 and 240 are, in
progressive time order, segments 222, 224, 226, 228, 242, 244, 246,
and 248. Each of these segments may be 400 chips in length, while
each of the pilot bursts 223, 227, 243, and 247 may be 96 chips in
length.
[0040] The access terminal 130 includes a receiver with the receive
circuitry 131, the decoder 134, and the equalizer 135. The
functioning of the access terminal and its components is controlled
by the processor 136 executing instruction stored in the memory
137. In operation, the receiver receives the forward link with the
frames 210, including the pilot bursts 223, 227, 243, and 247 in
the time slots 220/240. The access terminal uses the received pilot
bursts to train the equalizer 135, obtaining corresponding sets of
tap coefficients for demodulating the traffic in the traffic
carrying segments.
[0041] A single set of coefficients thus obtained, however, is not
necessarily used to demodulate the two traffic segments on either
side of the pilot burst that was used for obtaining the set of
coefficients. Instead, each segment is broken into multiple
sub-segments. As shown in FIG. 2, for example, each of the segments
is divided into two sub-segments, although a different number may
be used. The segment 222 is thus divided into sub-segments 222-1
and 222-2, the segment 224 is thus divided into sub-segments 224-1
and 224-2, and so on with appropriate changes to the segment
number. For demodulating at least some of these sub-segments, the
tap coefficients of the equalizer are determined by interpolating
the coefficients determined by equalizer training on the
immediately preceding and immediately following pilot bursts.
[0042] The coefficients may be linearly interpolated between those
determined for the successive (i.e., consecutive) pilot bursts. Let
us designate sets of coefficients determined (through training) for
the successive pilot bursts 223 and 227 as CT.sub.k and CT.sub.k+1,
respectively, where the subscripts refer to the time index of the
pilot bursts (which is the same as the index of the half-slot). Let
us also designate the set of equalizer tap coefficients used for
demodulating the sub-segments 224-1 as C.sub.k,1. This latter set
of coefficients can then be determined by linear interpolation over
time between CT.sub.k and CT.sub.k+1:
C.sub.k,1=(4/5)*CT.sub.k+(1/5)*CT.sub.k+1.
[0043] Designating the sets of equalizer coefficients used for
demodulating the sub-segments 224-2, 226-1, and 226-2 as C.sub.k,2,
C.sub.k,3, and C.sub.k,4, respectively, their values can be derived
as follows:
C.sub.k,2=(3/5)*CT.sub.k+(2/5)*CT.sub.k+1;
C.sub.k,3=(2/5)*CT.sub.k+(3/5)*CT.sub.k+1; and
C.sub.k,4=(1/5)*CT.sub.k+(4/5)*CT.sub.k+1.
[0044] Note that the second subscript j in the C.sub.k,j quantities
corresponds to the index of the specific sub-segment within the
time interval between the two successive pilot bursts 223 and 227.
The coefficients are thus interpolated substantially in a linear
manner. Linear interpolation of a coefficient applicable to a
sub-segment means that the coefficient is calculated by combining
weighted values of the coefficient of the same tap trained on the
pilot bursts immediately preceding and immediately following the
sub-segment; the weights given to the trained coefficients
immediately preceding and immediately following the coefficient
applicable to the sub-segment are inversely related to the distance
between the sub-segment and the immediately preceding and the
immediately following pilot burst. Thus, if the time distance
between the center of the sub-segment and the center of the
immediately preceding pilot burst is x, and the time distance
between the center of the sub-segment and the center of the
immediately following pilot burst is y, then the relative weight
given to the corresponding coefficient trained on the immediately
preceding pilot burst is (y/(x+y)), and the relative weight given
to the corresponding coefficient trained on the immediately
following pilot burst is (x/(x+y)). As illustrated in the above
example, this weighting relationship may be adhered to
substantially rather than precisely, with small deviations, for
example, due to quantization of time intervals (chip length).
[0045] It should be understood that the above formulas and other
descriptions of interpolation in this document imply the same type
of operation being performed on each of the individual coefficients
within each coefficient set. By way of explanatory example, assume
that each set of coefficients is represented by a vector of the
type {c.sub.j[1], c.sub.j[2] . . . c.sub.j[n]} where the subscript
is the sub-segment index and the bracketed quantity is the tap
index corresponding to the individual taps within the equalizer.
Assume also that CT.sub.k={ct.sub.k[1], ct.sub.k[2], . . .
ct.sub.k[n]}, where the bracketed quantity is also the tap index.
Assume further that CT.sub.k+1={ct.sub.k+1[1], ct.sub.k+1[2], . . .
ct.sub.k+1[n]}, where the bracketed quantity is again the tap
index. The coefficients corresponding to the same tap are
interpolated in the same way:
c.sub.1[m]=(4/5)*ct.sub.k[m]+(1/5)*ct.sub.k+1[m],
c.sub.2[m]=(3/5)*ct.sub.k[m]+(2/5)*ct.sub.k+1[m],
c.sub.3[m]=(2/5)*ct.sub.k[m]+(3/5)*ct.sub.k+1[m], and
[0046] c.sub.4[m]=(1/5)*ct.sub.k[m]+(4/5)*ct.sub.k+1[m], for all m
between 1 and the number representing the highest tap index in the
equalizer.
[0047] In some variants, the coefficients used for demodulating
sub-segments adjacent to a particular pilot burst (with its
accompanying MAC portions) are not interpolated, but instead the
coefficients obtained from training the equalizer for the pilot
burst are used directly for such subsegments. The immediately
preceding example would then be modified so that
C.sub.k,1=CT.sub.k, and C.sub.k,4=CT.sub.k+1, while C.sub.k,2 and
C.sub.k,3 are still interpolated as described above.
[0048] A tap shift may occur from one pilot burst training to a
following pilot burst training. This may be due to a change in the
center of mass or timing slide, which is the drift in the equalizer
center of mass time offset due to the coarse frequency offset
change between the base station and the access terminal over time.
For improved equalizer performance, it may be desirable to keep the
equalizer approximately centered, so that the strongest multipath
signals fall within a certain time span to the left and right of
the center of the adaptive finite impulse response filter. Tap
shifting logic, in combination with tap zeroing logic, may do this
job and shift the coefficients of the equalizer to left or right,
as needed to keep the equalizer approximately centered. Zero valued
tap coefficients may be shifted-in to fill the leading or trailing
taps, depending on the direction of the shift. This is used to
correct the timing of the equalizer. Tap shifting is described in
more detail in a commonly-assigned U.S. Pat. No. 7,012,952,
entitled Method and Apparatus for Adjusting Delay in Systems With
Time-Burst Pilot and Fractionally Spaced Equalizers.
[0049] Equalizer coefficients are then shifted in the correct
direction before a pilot training starts. In such cases, the
history is also shifted in the same manner, so that interpolation
of coefficients is done on correct indices. History in this context
means two sets of coefficients in memory from the previous two
pilot bursts.
[0050] The process of sub-segmentation need not necessarily be
performed so that each sub-segment is entirely contained within a
single segment, a single half-slot, or a single time slot. In
variants, a sub-segment may cross a segment boundary, a half-slot
boundary, or a time slot boundary. FIG. 3 illustrates an example
where a sub-segment crosses a time slot boundary (and also segment
and half-slot boundaries). As shown in FIG. 3, a time slot 320
includes half-slots 320A and 320B, with a pilot burst 323 in the
middle of the half-slot 320A, and another pilot burst 327 in the
middle of the half-slot 320B; a time slot 340 similarly has
half-slots 340A and 340B, with pilot bursts 343 and 347 in the
middle of each half-slot. Each of the pilot bursts 323/327/343/347
is surrounded by adjacent MAC portions 321. Each combination of a
pilot burst and its adjacent MAC portions breaks the corresponding
half-slot into two traffic carrying segments, which are, in
progressive time order, segments 322, 324, 326, 328, 342, 344, 346,
and 348. So far, this is essentially the same slot structure as
that shown in FIG. 2. Here, however, each set of two adjacent
segments is broken into five (an odd number) of sub-segments. The
segments 328 and 342 (which lie between pilot bursts 327 and 343,
and adjacent to each other) are now broken into sub-segments SBS-1,
SBS-2, SBS-3, SBS-4, and SBS-5. Note that SBS-3 straddles segment,
half-slot, and time slot boundaries.
[0051] The equalizer is again trained on the pilot bursts 327 and
343 to obtain sets of trained coefficients CT.sub.k and CT.sub.k+1,
respectively. To demodulate a particular sub-segment, a set of
coefficients is obtained by interpolating between the trained
coefficient sets surrounding the particular segment. For example,
the sets of coefficients C.sub.k,1 through C.sub.k,5 for
demodulating the sub-segments SBS-1 through SBS-5, respectively,
may be obtained as follows:
C.sub.k,1=(5/6)*CT.sub.k+(1/6)*CT.sub.k+1;
C.sub.k,2=(4/6)*CT.sub.k+(2/6)*CT.sub.k+1;
C.sub.k,3=(3/6)*CT.sub.k+(3/6)*CT.sub.k+1.
C.sub.k,4=(2/6)*CT.sub.k+(4/6)*CT.sub.k+1; and
C.sub.k,5=(1/6)*CT.sub.k+(5/6)*CT.sub.k+1.
[0052] Again, it may be preferred not to interpolate the
coefficients for the sub-segments immediately adjacent to the pilot
burst, but rather use the sets of trained coefficients obtained for
the adjacent pilot bursts to demodulate the particular
sub-segments. For example, C.sub.k,1 may then be set to CT.sub.k,
C.sub.k,5 may be set to CT.sub.k+1, and C.sub.k,2 through C.sub.k,4
may be interpolated as described above. More generally,
coefficients for only some selected sub-segments may be obtained
through interpolation of the trained coefficients surrounding the
segments. Of course, as illustrated above, all of the coefficients
may be interpolated.
[0053] While FIGS. 2 and 3 illustrate division of traffic segments
into equal sub-segments, this need not always be the case. Some
processes and systems use division into sub-segments not all of
which are equal. Moreover, equalization need not be carried out for
all data in the segments. In some systems, equalization is not
performed for preambles within the traffic segments. In this case,
there may be no need to include the preambles in the
sub-segmentation process, or to perform interpolation for
sub-segments that have only preamble data.
[0054] The received signal's SINR is sometimes used in processing
the received signal.
[0055] SINR measurement is described in more detail in a
commonly-assigned U.S. Pat. No. 7,106,792, entitled Method and
Apparatus for Estimating the Signal to Interference-Plus-Noise
Ratio of a Wireless Channel.
[0056] The received signal's SINR measured during pilot bursts may
also be interpolated for the sub-segments and then used in
processing the information in the traffic segments. For example,
the SINR may be interpolated for scaling equalizer output before
feeding the output to a block that calculates log likelihood ratio
(LLR). SINR interpolation may be done in the same ways as are
described throughout this document in relation to tap coefficients.
Referring again to FIG. 3, let us designate the SINR measurements
for pilot bursts 327 and 343 as SM.sub.k and SM.sub.k+1,
respectively. Then, the interpolated SINR values SI.sub.k,1 through
SI.sub.k,5 for processing the sub-segments SBS-1 through SBS-5,
respectively, may be obtained as follows:
SI.sub.k,1=(5/6)*SM.sub.k+(1/6)*SM.sub.k+1;
SI.sub.k,2=(4/6)*SM.sub.k+(2/6)*SM.sub.k+1;
SI.sub.k,3=(3/6)*SM.sub.k+(3/6)*SM.sub.k+1.
SI.sub.k,4=(2/6)*SM.sub.k+(4/6)*SM.sub.k+1; and
SI.sub.k,5=(1/6)*SM.sub.k+(5/6)*SM.sub.k+1.
[0057] SINR interpolation may be carried out in the linear
domain/scale, as opposed to logarithmic or decibel domain/scale. If
for example, the SINR measurements SM.sub.k and SM.sub.k+1 are
made, stored, or otherwise available in decibels, they may first be
converted to linear scale. Interpolation of the linear values may
then be carried out, and the interpolated results may be converted
into decibels and stored as decibel values.
[0058] As a person skilled in the art would understand after
perusal of this document, the meaning of "linear" as applied to
domain or scale is not the same as the meaning of "linear" as
applied to the interpolation process itself. SINR may be
interpolated in the linear domain using a non-linear interpolation
method, for example.
[0059] SINR values for only some selected sub-segments may be
obtained through interpolation of the SINR measurements obtained
for pilot bursts. For example, SINR values used in processing of
sub-segments immediately adjacent to a particular pilot burst may
be set to the measured SINR value for the same particular pilot
burst. Of course, as illustrated above, all of the SINR values may
be interpolated.
[0060] FIG. 4 illustrates selected steps of a process 400 for
operating a receiver with tap coefficients and SINR interpolation.
At flow point 401, the receiver is operational and configured to
receive time-slots with pilot bursts in the middle of each
half-slot, and traffic segments in at least parts of the remaining
portions of the half-slots.
[0061] In step 405, a first half-slot is received, including a
first pilot burst in the middle of the first half-slot and a first
traffic segment following the first half-slot.
[0062] In step 410, an equalizer of the receiver is trained based
on the first pilot burst to obtain a first set of trained equalizer
coefficients.
[0063] In step 415, a first measured SINR is determined based on
the first pilot burst.
[0064] In step 420, a second half-slot is received, including a
second pilot burst in the middle of the second half-slot and a
second traffic segment following the second half-slot.
[0065] In step 425, the equalizer of the receiver is trained based
on the second pilot burst to obtain a second set of trained
equalizer coefficients.
[0066] In step 430, a second measured SINR is determined based on
the second pilot burst.
[0067] In step 435, the first and the second traffic segments are
sub-segmented (divided) into three or more sub-segments.
[0068] In step 440, equalizer coefficients are interpolated between
the first and the second set to obtain a set of interpolated
coefficients for one or more of the sub-segments.
[0069] In step 445, SINR is interpolated between the first and the
second measured SINR values to obtain interpolated SINR value or
values for one or more of the sub-segments.
[0070] In step 450, the traffic in the sub-segments is equalized
using the tap coefficients applicable to each sub-segment. The
applicable tap-coefficients for at least one of the sub-segments
have been determined by interpolation in the step 440. The traffic
in the sub-segments is then demodulated.
[0071] In step 455, the demodulated traffic in the sub-segments is
processed using the SINR values applicable to each sub-segment. For
example, equalizer output is scaled using the SINR values. The
applicable SINR for at least one of the sub-segments has been
determined by interpolation in the step 445.
[0072] The process 400 then terminates at flow point 499. It should
be noted that the process would typically be repeated with receipt
of the following half-slots. Moreover, some of the steps (or
results obtained in the steps) of one instance of the process 400
may be reused in the following instance of the same process.
[0073] SINR interpolation and tap coefficient interpolation may be
practiced separately or together. Thus, a system may employ tap
coefficient interpolation without SINR interpolation, it may employ
SINR interpolation without tap coefficient interpolation, or it may
employ both tap coefficient and SINR interpolation. In the latter
case, the tap coefficients and SINR may be interpolated in the same
way and over the same sub-segments; alternatively, they may be
interpolated in different ways and/or over different
sub-segments.
[0074] While the above examples illustrate linear or substantially
linear interpolation, other kinds of interpolation may be used, for
example, polynomial interpolation, including cubic interpolation.
Averaging technique may also be used. Averaging means the use of
the average of the coefficient values trained on successive pilot
bursts for a given tap for all sub-segments lying between the
successive pilot bursts. For coefficient interpolation, linear
interpolation may be combined with averaging of coefficients. The
following formula may be used for determining a given tap
coefficient c'.sub.k for a sub-segment between two successive pilot
bursts designated with half-slot time indices [n-2] (the earlier in
time index) and [n-1] (the index following in time):
c k ' = Avg 2 * [ c k [ n - 1 ] + c k [ n - 2 ] ] + ( 1 - Avg ) 2
10 * [ .alpha. * c k [ n - 2 ] + ( 2 10 - .alpha. ) * c k [ n - 1 ]
] ##EQU00001##
[0075] The above formula assumes 1024 (2.sup.10) chip distance
between pilot bursts, and hence the appearance of the 2.sup.10
value for the time distance. In the formula, c.sub.k[n-1] and
c.sub.k[n-2] stand, respectively, for the values of the given tap
coefficient trained on the pilot bursts in the [n-1] and [n-2]
half-slots; the interpolation factor .alpha. is the distance from
the center of the sub-segment to the center of the pilot burst at
index [n-1]; and Avg is the averaging factor that balances the
weight of averaging (or smoothing) and linear interpolation. For
instance, Avg=0 reduces the formula to linear interpolation only,
Avg=1 reduces the formula to averaging only, whereas Avg=0.5 gives
equal weight to averaging and linear interpolation.
[0076] A non-exclusive example of different kinds of interpolation
is where the system interpolates the tap coefficients linearly,
while using cubic interpolation for SINR. Another non-exclusive
example is where the system interpolates linearly only the tap
coefficients for sub-segments that are not adjacent to pilot
bursts, while interpolating SINR for all sub-segments using cubic
interpolation. Still another non-exclusive example is where the
system uses a greater number of sub-segments for SINR interpolation
than the number of sub-segments it uses for coefficient
interpolation. Many other examples are of course also possible.
[0077] The processes and systems described in this document may be
used in data-optimized systems, that is, systems optimized for data
transmission (as opposed to voice transmission), and in particular
such systems are optimized for downlink (forward link) data
transmission. Data-optimized systems need not exclude uplink
(reverse link) data transmission, or voice transmission in either
direction. It should be noted that voice may be transmitted as
data, for example, in the case of voice over internet protocol
(VoIP) transmissions. The processes and systems may also be used in
data-only systems, that is, systems used for data transmission
only. Still further, the processes and systems may be used in voice
transmission as such, that is, voice transmission not using
VoIP.
[0078] The processes and systems described may be used in access
terminals of a wireless cellular communication system. The
processes and systems may also (or instead) be used on the radio
network side of the wireless cellular communication system, for
example, in a base transceiver station. The process and systems may
be used with or without a Rake receiver.
[0079] In some systems, steps for interpolating equalizer
coefficients are stored in firmware, while in other systems, the
steps are stored in software. These storage selections, however,
are not necessarily required in all systems.
[0080] Although steps and decisions of various methods may have
been described serially in this disclosure, some of these steps and
decisions may be performed by separate elements in conjunction or
in parallel, asynchronously or synchronously, in a pipelined
manner, or otherwise. There is no particular requirement that the
steps and decisions be performed in the same order in which this
description lists them, except where explicitly so indicated,
otherwise made clear from the context, or inherently required. It
should be noted, however, that in selected variants the steps and
decisions are performed in the particular sequences described above
and/or shown in the accompanying Figures. Furthermore, not every
illustrated step and decision may be required in every system in
accordance with the invention, while some steps and decisions that
have not been specifically illustrated may be desirable or
necessary in some systems in accordance with the invention.
[0081] Those of skill in the art would also understand that
information and signals may be represented using any of a variety
of different technologies and techniques. For example, data,
instructions, commands, information, signals, bits, symbols, and
chips that may be referenced throughout the above description may
be represented by voltages, currents, electromagnetic waves,
magnetic fields or particles, optical fields or particles, or any
combination thereof.
[0082] Those of skill would further appreciate that the various
illustrative logical blocks, modules, circuits, and algorithm steps
described in connection with the embodiments disclosed herein may
be implemented as electronic hardware, computer software, or
combinations of both. To show clearly this interchangeability of
hardware and software, various illustrative components, blocks,
modules, circuits, and steps may have been described above
generally in terms of their functionality. Whether such
functionality is implemented as hardware, software, or combination
of hardware and software depends upon the particular application
and design constraints imposed on the overall system. Skilled
artisans may implement the described functionality in varying ways
for each particular application, but such implementation decisions
should not be interpreted as causing a departure from the scope of
the present invention.
[0083] The various illustrative logical blocks, modules, and
circuits described in connection with the embodiments disclosed
herein may be implemented or performed with a general purpose
processor, a digital signal processor (DSP), an application
specific integrated circuit (ASIC), a field programmable gate array
(FPGA) or other programmable logic device, discrete gate or
transistor logic, discrete hardware components, or any combination
thereof designed to perform the functions described herein. A
general purpose processor may be a microprocessor, but in the
alternative, the processor may be any processor, controller,
microcontroller, or state machine. A processor may also be
implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0084] The steps of a method or algorithm that may have been
described in connection with the embodiments disclosed herein may
be embodied directly in hardware, in a software module executed by
a processor, or in a combination of the two. A software module may
reside in RAM memory, flash memory, ROM memory, EPROM memory,
EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or
any other form of storage medium known in the art. An exemplary
storage medium is coupled to the processor such that the processor
can read information from, and write information to, the storage
medium. In the alternative, the storage medium may be integral to
the processor. The processor and the storage medium may reside in
an ASIC. The ASIC may reside in an access terminal. Alternatively,
the processor and the storage medium may reside as discrete
components in an access terminal.
[0085] The previous description of the disclosed embodiments is
provided to enable any person skilled in the art to make or use the
present invention. Various modifications to these embodiments will
be readily apparent to those skilled in the art, and the generic
principles defined herein may be applied to other embodiments.
Thus, the present invention is not intended to be limited to the
embodiments shown herein, but is to be accorded the widest scope
consistent with the principles and novel features disclosed
herein.
* * * * *